GENERAL INFORMATION
The anatomical snuff box is a triangular depression on the lateral aspect of the wrist. It is visible when the thumb is extended. The tendons of the extensor muscles of the thumb form it. Historically, people would place powdered tobacco (snuff) in this depression, hence the name. This area is essential in both anatomical studies and clinical settings, as it houses several vital structures. It includes blood vessels and bones, making it a critical landmark for wrist injuries and fractures.
BOUNDARIES
The following tendons define the anatomical snuff box:
- Lateral Boundary (Radial Side): Formed by the tendon of the abductor pollicis longus and the tendon of the extensor pollicis brevis.
- Medial Boundary (Ulnar Side): Formed by the tendon of the extensor pollicis longus.
- Proximal Boundary: The styloid process of the radius marks the upper boundary of the anatomical snuff box.
- Floor: The floor of the snuff box is formed by the scaphoid and trapezium bones, as well as the base of the first metacarpal.
CONTENTS
The anatomical snuff box contains several vital structures:
- Radial Artery: The most important structure within the anatomical snuff box is that it runs diagonally across the floor of the snuff box. It makes an essential site for measuring the radial pulse.
- Cephalic Vein: This superficial vein runs along the lateral side of the arm and may be visible over the snuff box.
- Superficial Branch of the Radial Nerve: Provides sensation to the back of the hand. Specifically the thumb and index finger and crosses over the snuff box area.
MAJOR ARTERIES
The main artery in the anatomical snuff box is:
- Radial Artery: This artery runs across the floor of the snuff box and is crucial for vascular examination. It can be palpated here, making it a helpful landmark for taking the radial pulse.
NEURAL INNERVATION
The anatomical snuff box is innervated by:
- Superficial Branch of the Radial Nerve: This nerve crosses the snuff box, providing sensory innervation to the skin over the thumb, index finger and back of the hand.
CLINICAL SIGNIFICANCE
The anatomical snuff box is a clinically significant landmark for the following reasons:
- Scaphoid Fracture: One of the most common injuries associated with this region is a fracture of the scaphoid bone. Tenderness in the anatomical snuff box following a fall on an outstretched hand may indicate a scaphoid fracture, which can be confirmed with imaging.
- Radial Artery Pulse: The radial artery can be palpated in the anatomical snuff box, making it an accessible site for checking the pulse or drawing blood in clinical practice.
- De Quervain’s Tenosynovitis: This condition involves inflammation of the tendons of the abductor pollicis longus and extensor pollicis brevis, both of which form the lateral boundary of the anatomical snuff box. This condition leads to pain and tenderness in the area.
TRIGGER POINT
Trigger points in the thumb extensors or overuse injuries can cause pain in the anatomical snuff box region. Particularly in the tendons that border the snuff box. These trigger points may cause referred pain in the thumb, wrist and hand. It may lead to discomfort during thumb extension or gripping activities.
CONCENTRIC FUNCTION
The tendons that form the anatomical snuff box contract concentrically to produce movements such as:
- Thumb Extension: The tendons of the extensor pollicis brevis and extensor pollicis longus extend the thumb at the metacarpophalangeal and interphalangeal joints.
- Thumb Abduction: The abductor pollicis longus assists in moving the thumb away from the palm, allowing for grasping and pinching.
ECCENTRIC FUNCTION
The muscles of the anatomical snuff box play a role in controlling thumb movements during eccentric contraction:
- Thumb Flexion Control: The tendons of the extensor muscles control the flexion of the thumb, preventing it from moving too quickly toward the palm during gripping.
ISOMETRIC FUNCTION
The tendons of the anatomical snuff box muscles engage isometrically to stabilise the thumb during static tasks:
- Thumb Stability: These muscles maintain the thumb’s position during gripping tasks. It allows for a firm grip while stabilising the wrist and hand.
RELATED MUSCLES SCIENTIFIC NAMES
- Abductor Pollicis Longus: Abducts the thumb, forming the lateral border of the anatomical snuff box.
- Extensor Pollicis Brevis: Extends the thumb and forms part of the lateral boundary of the snuff box.
- Extensor Pollicis Longus: Extends the thumb and forms the medial border of the snuff-box, assisting in thumb movements and wrist stabilisation.
ANTAGONIST
- Flexor Pollicis Longus: Flexes the thumb, opposing the extension provided by the extensor pollicis longus and brevis during thumb movements.
- Adductor Pollicis: Opposes the abduction performed by the abductor pollicis longus, assisting in bringing the thumb back towards the palm.
COMMON INJURIES
- Scaphoid Fracture: A break in the scaphoid bone, often caused by falling on an outstretched hand, resulting in pain and tenderness in the anatomical snuff box. It requires prompt treatment to avoid complications such as avascular necrosis.
- De Quervain’s Tenosynovitis: Inflammation of the tendons of the abductor pollicis longus and extensor pollicis brevis, causing pain along the lateral border of the snuff-box, especially during thumb movements.
- Radial Artery Injury: Injury to the radial artery within the snuff box can result in compromised blood flow to the hand and requires immediate medical attention.
EXERCISES
- Thumb Extensions with Resistance Band: Strengthens the extensor muscles that form the anatomical snuff box. It helps improve thumb mobility and extension control.
- Radial Deviations with Weight: Engages the muscles and tendons involved in the anatomical snuff box by moving the wrist toward the thumb side. It helps to improve strength and mobility.
- Thumb Abductions: Targets the abductor pollicis longus by moving the thumb away from the palm, enhancing thumb strength and flexibility.
- Wrist Curls: Focuses on strengthening the wrist extensors, supporting the tendons that form the boundaries of the anatomical snuff box and improving overall wrist stability.
- Grip Strengthening with Wrist Extension: Involves gripping and releasing objects while extending the wrist. It engages the muscles around the anatomical snuff box to improve hand and wrist strength.
STRETCHES
- Thumb Extensor Stretch: Involves gently pulling the thumb backwards to stretch the tendons of the extensor pollicis longus and brevis. It helps relieve tension in the muscle.
- Wrist Extensor Stretch: Performed by extending the arm and pulling the fingers downward with the opposite hand, stretching the wrist extensors and improving flexibility in the snuff box area.
- Radial Nerve Stretch: Helps relieve tension in the anatomical snuff box by gently extending the arm and rotating the wrist. It promotes nerve mobility and reduces strain.
- Wrist Flexor Stretch: Targets the wrist flexors by pulling the hand back with the opposite hand, balancing the tension between flexors and extensors.
- Thumb Flexor Stretch: Stretches the flexor pollicis longus, balancing the extension provided by the thumb extensors and relieving tension in the snuff box region.
